Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/386—Silicon or alloys based on silicon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/32—Compounds containing nitrogen bound to oxygen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/54—Silicon-containing compounds
  • C08K5/541—Silicon-containing compounds containing oxygen
  • C08K5/5415—Silicon-containing compounds containing oxygen containing at least one Si—O bond
  • C08K5/5419—Silicon-containing compounds containing oxygen containing at least one Si—O bond containing at least one Si—C bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/04—Ingredients treated with organic substances
  • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/364—Composites as mixtures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2361/00—Characterised by the use of condensation polymers of aldehydes or ketones; Derivatives of such polymers
  • C08J2361/04—Condensation polymers of aldehydes or ketones with phenols only
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2379/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen with or without oxygen, or carbon only, not provided for in groups C08J2361/00 - C08J2377/00
  • C08J2379/04—Polycondensates having nitrogen-containing heterocyclic rings in the main chain; Polyhydrazides; Polyamide acids or similar polyimide precursors
  • C08J2379/08—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K2003/023—Silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present application relates generally to silicon particles.
• the present application relates to silicon particles and composite materials including silicon particles for use in battery electrodes. Description of the Related Art
• a lithium ion battery typically includes a separator and/or electrolyte between an anode and a cathode.
• the separator, cathode and anode materials are individually formed into sheets or films. Sheets of the cathode, separator and anode are subsequently stacked or rolled with the separator separating the cathode and anode (e.g., electrodes) to form the battery.
• Typical electrodes include electro-chemically active material layers on electrically conductive metals (e.g., aluminum and copper). Films can be rolled or cut into pieces which are then layered into stacks. The stacks are of alternating electro-chemically active materials with the separator between them.
• a method of forming a composite material film can include providing a mixture comprising a precursor and silane- treated silicon particles.
• the method can also include pyrolysing the mixture to convert the precursor into one or more carbon phases to form the composite material film with the silicon particles distributed throughout the composite material film.
• the silane-treated silicon particles can comprise silicon particles treated with one or more organosilanes.
• the silane- treated silicon particles can comprise silicon oxide surfaces reacted with the one or more organosilanes.
• one or more organosilanes can comprise one or more silanols, silyl ethers, silyl chlorides, dialkylaminosilanes, silyl hydrides, or cyclic azasilanes.
• one or more organosilanes can comprise one or more aminoalkyl functional groups.
• one or more organosilanes can comprise 3- aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, or 2,2- dimethoxy-1,6-diaza-2-silacyclooctane.
• the precursor can comprise polyimide.
• one or more organosilanes can comprise an epoxide linker.
• the epoxide linker can comprise 5,6-epoxyhexyltriethoxysilane.
• the precursor can comprise a phenolic resin.
• one or more organosilanes can comprise an aromatic functional group.
• one or more organosilanes can comprise benzyltriethoxysilane.
• the precursor can comprise polycyclic aromatic hydrocarbon.
• one or more organosilanes can comprise dodecylsilane.
• one or more organosilanes can comprise (N, N- dimethylamino)trimethylsilane.
• the silicon particles can be suspended in liquid comprising the one or more organosilanes.
• the silicon particles can be exposed to one or more organosilane vapors.
• the mixture can comprise one or more organosilanes.
• the composite material film can comprise the silicon particles at about 50% to about 99% by weight.
• the composite material film can be electrochemically active.
• One or more types of carbon phases can be a continuous phase that holds the composite material film.
• a method of forming a battery electrode is disclosed.
• the electrode can include the composite material film described herein.
• the electrode can be an anode.
• Figure 1A illustrates an embodiment of a method of forming a composite material that includes forming a mixture that includes a precursor, casting the mixture, drying the mixture, curing the mixture, and pyrolyzing the precursor;
• Figure 1B is a schematic illustration of the formation of silicon carbide on a silicon particle
• Figures 2A and 2B are SEM micrographs of one embodiment of micron- sized silicon particles milled-down from larger silicon particles;
• Figures 2C and 2D are SEM micrographs of one embodiment of micron- sized silicon particles with nanometer-sized features on the surface;
• Figure 2E illustrates an example embodiment of a method of forming a composite material
• Figure 3A schematically illustrates an example silane-treated silicon particle
• Figure 3B illustrates an example embodiment of a method of forming a composite material
• Figure 4 is a plot of the discharge capacity at an average rate of C/2.6
• Figure 5 is a plot of the discharge capacity at an average rate of C/3;
• Figure 6 is a plot of the discharge capacity at an average rate of C/3.3
• Figure 7 is a plot of the discharge capacity at an average rate of C/5;
• Figure 8 is a plot of the discharge capacity at an average rate of C/9
• Figure 9 is a plot of the discharge capacity
• Figure 10 is a plot of the discharge capacity at an average rate of C/9
• Figures 11A and 11B are plots of the reversible and irreversible capacity as a function of the various weight percentage of PI derived carbon from 2611c and graphite particles for a fixed percentage of 20 wt. % Si;
• Figure 12 is a plot of the first cycle discharge capacity as a function of weight percentage of carbon
• Figure 13 is a plot of the reversible (discharge) and irreversible capacity as a function of pyrolysis temperature
• Figure 14 is a photograph of a 4.3 cm x 4.3 cm composite anode film without a metal foil support layer
• Figure 15 is a scanning electron microscope (SEM) micrograph of a composite anode film before being cycled (the out-of-focus portion is a bottom portion of the anode and the portion that is in focus is a cleaved edge of the composite film);
• Figure 16 is another SEM micrograph of a composite anode film before being cycled
• Figure 17 is a SEM micrograph of a composite anode film after being cycled 10 cycles
• Figure 18 is another SEM micrograph of a composite anode film after being cycled 10 cycles
• Figure 19 is a SEM micrograph of a composite anode film after being cycled 300 cycles;
• Figure 20 includes SEM micrographs of cross-sections of composite anode films
• Figure 21 is an x-ray powder diffraction (XRD) graph of the sample silicon particles
• Figure 22 is a SEM micrograph of one embodiment of silicon particles
• Figure 23 is another SEM micrographs of one embodiment of silicon particles
• Figure 24 is a SEM micrograph of one embodiment of silicon particles
• Figure 25 is a SEM micrograph of one embodiment of silicon particles
• Figure 26 is a chemical analysis of the sample silicon particles
• Figures 27A and 27B are example particle size histograms of two micron- sized silicon particles with nanometer-sized features
• Figure 28 is a plot of discharge capacity during cell cycling comparing two types of example silicon particles;
• Figure 29 shows X-ray Photoelectron Spectroscopy (XPS) spectra of example silane-treated and untreated silicon particles;
• Figure 30A is a scanning electron microscope with focused ion beam (SEM-FIB) micrograph of a cross-section of an example silicon-carbon composite material made with untreated silicon particles;
• Figure 30B is a SEM-FIB micrograph of a cross-section of an example silicon-carbon composite material made with silane-treated silicon particles;
• Figure 31 shows a graph of capacity retention versus cycle number for full-cells comprising silane-treated silicon particles compared with full-cells comprising untreated silicon particles;
• Figure 32 shows a graph of capacity retention versus cycle number for full-cells comprising silane-treated silicon particles compared with full-cells comprising untreated silicon particles in a follow-up trial.
• Silicon-carbon composite electrodes can include silicon particles suspended in a carbon matrix.
• the electrodes can include the composite material as a self-supported structure or attached to a current collector.
• Silicon-carbon electrodes can provide superior energy density compared with industry-standard graphite electrodes.
• Silicon-carbon electrodes can also have superior cycle life and initial coulombic efficiency compared with silicon electrodes comprised of silicon particles, conductive additives, and polymeric binders.
• silicon particles can be suspended in an organic thermoplastic or thermoset binder and formed into a free-standing film, which can then be thermally treated to convert the organic material into carbon.
• the carbon matrix can act as an electrically conductive structural component which can hold the electrode together.
• the silicon particles may be wetted (e.g., substantially wetted or fully wetted in some cases) by the carbon precursor (e.g., to achieve increased and/or maximum interfacial contact), and for the precursor to adhere strongly with the silicon particles.
• the silicon particles are not wetted by the carbon precursor, voids and/or porosity may appear at the interface between the silicon and the carbon, which may negatively impact the strength and conductivity of the composite.
• silicon particles with customized surface chemistry may be used to improve the wetting by matching surface energy with the carbon precursor, and can promote strong adhesion by providing reactive sites on the silicon particle surface to enable one or more bonding interactions with the carbon precursor, such as pi-stacking, dipole-dipole interaction, hydrogen bonding, and/or covalent bonding.
• Typical carbon anode electrodes include a current collector such as a copper sheet. Carbon is deposited onto the collector along with an inactive binder material. Carbon is often used because it has excellent electrochemical properties and is also electrically conductive. If the current collector layer (e.g., copper layer) was removed, the carbon would likely be unable to mechanically support itself. Therefore, conventional electrodes require a support structure such as the collector to be able to function as an electrode.
• the electrode (e.g., anode or cathode) compositions described in this application can produce electrodes that are self-supported. The need for a metal foil current collector is eliminated or minimized because conductive carbonized polymer is used for current collection in the anode structure as well as for mechanical support.
• a metal current collector is typically added to ensure sufficient rate performance.
• the carbonized polymer can form a substantially continuous conductive carbon phase in the entire electrode as opposed to particulate carbon suspended in a non-conductive binder in one class of conventional lithium-ion battery electrodes.
• Advantages of a carbon composite blend that utilizes a carbonized polymer can include, for example, 1) higher capacity, 2) enhanced overcharge/discharge protection, 3) lower irreversible capacity due to the elimination (or minimization) of metal foil current collectors, and 4) potential cost savings due to simpler manufacturing.
• Anode electrodes currently used in the rechargeable lithium-ion cells typically have a specific capacity of approximately 200 milliamp hours per gram (including the metal foil current collector, conductive additives, and binder material).
• Graphite the active material used in most lithium ion battery anodes, has a theoretical energy density of 372 milliampere hours per gram (mAh/g).
• silicon has a high theoretical capacity of 4200 mAh/g.
• silicon may be used as the active material for the cathode or anode.
• silicon nanopowders e.g., silicon nanopowders, silicon nanowires, porous silicon, and ball-milled silicon
• small particle sizes generally can increase cycle life performance. They also can display very high irreversible capacity. However, small particle sizes also can result in very low volumetric energy density (for example, for the overall cell stack) due to the difficulty of packing the active material. Larger particle sizes, (for example, sizes in the micrometer or micron range) generally can result in higher density anode material.
• the expansion of the silicon active material can result in poor cycle life due to particle cracking. For example, silicon can swell in excess of 300% upon lithium insertion. Because of this expansion, anodes including silicon should be allowed to expand while maintaining electrical contact between the silicon particles.
• the converted polymer also acts as an expansion buffer for silicon particles during cycling so that a high cycle life can be achieved.
• the resulting electrode is an electrode that is comprised substantially of active material.
• the resulting electrode is substantially active material.
• the electrodes can have a high energy density of between about 500 mAh/g to about 3500 mAh/g that can be due to, for example, 1) the use of silicon, 2) elimination or substantial reduction of metal current collectors, and 3) being comprised entirely or substantially entirely of active material.
• carbonized polymer may react with a native silicon oxide surface layer on the silicon particles.
• the surface of the particles is modified to form a surface coating thereon, which may further act as an expansion buffer for silicon particles during cycling.
• the surface coating may include silicon carbide.
• the composite materials described herein can be used as an anode in most conventional lithium ion batteries; they may also be used as the cathode in some electrochemical couples with additional additives.
• the composite materials can also be used in either secondary batteries (e.g., rechargeable) or primary batteries (e.g., non-rechargeable).
• the composite materials are self-supported structures.
• the composite materials are self-supported monolithic structures.
• a collector may be included in the electrode comprised of the composite material.
• the composite material can be used to form carbon structures discussed in U.S. Patent Application Number 12/838,368 (U.S. Patent Application Publication No.
• the composite materials described herein can be, for example, silicon composite materials, carbon composite materials, and/or silicon-carbon composite materials.
• certain embodiments can further include composite materials including micron-sized silicon particles.
• the micron-sized silicon particles have nanometer-sized features on the surface.
• Silicon particles with such a geometry may have the benefits of both micron-sized silicon particles (e.g., high energy density) and nanometer-sized silicon particles (e.g., good cycling behavior).
• micron-sized silicon particles e.g., high energy density
• nanometer-sized silicon particles e.g., good cycling behavior
• the term“silicon particles” in general can include micron-sized silicon particles with or without nanometer-sized features.
• Some composite materials may be provided on a current collector.
• the composite material can be attached to a current collector using an attachment substance.
• the attachment substance and current collector may be any of those known in the art or yet to be developed.
• some composite materials can be provided on a current collector as described in U.S. Patent Application No. 13/333,864 (U.S. Patent No. 9,397,338), entitled“Electrodes, Electrochemical Cells, and Methods of Forming Electrodes and Electrochemical Cells;” or U.S. Patent Application No. 13/796,922 (U.S. Patent No.
• Figure 1A illustrates one embodiment of a method of forming a composite material 100.
• the method of forming a composite material can include forming a mixture including a precursor, block 101.
• the method can further include pyrolyzing the precursor to convert the precursor to a carbon phase.
• the precursor mixture may include carbon additives such as graphite active material, chopped or milled carbon fiber, carbon nanofibers, carbon nanotubes, and/or other carbons.
• the resulting carbon material can be a self-supporting monolithic structure.
• one or more materials are added to the mixture to form a composite material. For example, silicon particles can be added to the mixture.
• the carbonized precursor results in an electrochemically active structure that holds the composite material together.
• the carbonized precursor can be a substantially continuous phase.
• the silicon particles including micron-sized silicon particles with or without nanometer-sized features, may be distributed throughout the composite material.
• the carbonized precursor can be a structural material as well as an electro-chemically active and electrically conductive material.
• material particles added to the mixture are homogenously or substantially homogeneously distributed throughout the composite material to form a homogeneous or substantially homogeneous composite.
• the mixture can include a variety of different components.
• the mixture can include one or more precursors.
• the precursor is a hydrocarbon compound.
• the precursor can include polyamideimide, polyamic acid, polyimide, etc.
• Other precursors can include phenolic resins, epoxy resins, and/or other polymers.
• the mixture can further include a solvent.
• the solvent can be N- methyl-pyrrolidone (NMP).
• NMP N- methyl-pyrrolidone
• Other possible solvents include acetone, diethyl ether, gamma butyrolactone, isopropanol, dimethyl carbonate, ethyl carbonate, dimethoxyethane, ethanol, methanol, etc.
• precursor and solvent solutions examples include PI-2611 (HD Microsystems), PI-5878G (HD Microsystems) and VTEC PI-1388 (RBI, Inc.).
• PI-2611 is comprised of >60% n-methyl-2-pyrrolidone and 10-30% s-biphenyldianhydride/p- phenylenediamine.
• PI-5878G is comprised of >60% n-methylpyrrolidone, 10-30% polyamic acid of pyromellitic dianhydride/oxydianiline, 10-30% aromatic hydrocarbon (petroleum distillate) including 5-10% 1,2,4-trimethylbenzene.
• the amount of precursor in the solvent is about 10 wt.
• % to about 30 wt. % Additional materials can also be included in the mixture.
• silicon particles or carbon particles including graphite active material, chopped or milled carbon fiber, carbon nanofibers, carbon nanotubes, graphene, and other conductive carbons can be added to the mixture.
• the mixture can be mixed to homogenize the mixture.
• the mixture is cast on a substrate, block 102 in Figure 1A.
• casting includes using a gap extrusion, tape casting, or a blade casting technique.
• the blade casting technique can include applying a coating to the substrate by using a flat surface (e.g., blade) which is controlled to be a certain distance above the substrate.
• a liquid or slurry can be applied to the substrate, and the blade can be passed over the liquid to spread the liquid over the substrate.
• the thickness of the coating can be controlled by the gap between the blade and the substrate since the liquid passes through the gap. As the liquid passes through the gap, excess liquid can also be scraped off.
• the mixture can be cast on a substrate comprising a polymer sheet, a polymer roll, and/or foils or rolls made of glass or metal.
• the mixture can then be dried to remove the solvent, block 103.
• a polyamic acid and NMP solution can be dried at about 110 °C for about 2 hours to remove the NMP solution.
• the dried mixture can then be removed from the substrate.
• an aluminum substrate can be etched away with HCl.
• the dried mixture can be removed from the substrate by peeling or otherwise mechanically removing the dried mixture from the substrate.
• the substrate comprises polyethylene terephthalate (PET), including for example Mylar®.
• the dried mixture is a film or sheet.
• the dried mixture is optionally cured, block 104.
• the dried mixture may be further dried.
• the dried mixture can placed in a hot press (e.g., between graphite plates in an oven).
• a hot press can be used to further dry and/or cure and to keep the dried mixture flat.
• the dried mixture from a polyamic acid and NMP solution can be hot pressed at about 200 °C for about 8 to 16 hours.
• the entire process including casting and drying can be done as a roll-to-roll process using standard film-handling equipment.
• the dried mixture can be rinsed to remove any solvents or etchants that may remain.
• DI de-ionized
• tape casting techniques can be used for the casting.
• the mixture can be coated on a substrate by a slot die coating process (e.g., metering a constant or substantially constant weight and/or volume through a set or substantially set gap).
• a slot die coating process e.g., metering a constant or substantially constant weight and/or volume through a set or substantially set gap.
• the dried mixture may be cut or mechanically sectioned into smaller pieces.
• the mixture further goes through pyrolysis to convert the polymer precursor to carbon, block 105.
• the mixture is pyrolysed in a reducing atmosphere.
• a reducing atmosphere for example, an inert atmosphere, a vacuum and/or flowing argon, nitrogen, or helium gas can be used.
• the mixture is heated to about 900 °C to about 1350 °C.
• polyimide formed from polyamic acid can be carbonized at about 1175 °C for about one hour.
• the heat up rate and/or cool down rate of the mixture is about 10°C/min.
• a holder may be used to keep the mixture in a particular geometry. The holder can be graphite, metal, etc.
• the mixture is held flat.
• tabs can be attached to the pyrolysed material to form electrical contacts. For example, nickel, copper or alloys thereof can be used for the tabs.
• one or more of the methods described herein can be carried out in a continuous process.
• casting, drying, possibly curing and pyrolysis can be performed in a continuous process.
• the mixture can be coated onto a glass or metal cylinder.
• the mixture can be dried while rotating on the cylinder to create a film.
• the film can be transferred as a roll or peeled and fed into another machine for further processing. Extrusion and other film manufacturing techniques known in industry could also be utilized prior to the pyrolysis step.
• a carbon material e.g., at least one carbon phase
• the carbon material is a hard carbon.
• the precursor is any material that can be pyrolysed to form a hard carbon.
• a composite material can be created.
• the mixture can include silicon particles, creating a silicon-carbon (e.g., at least one first phase comprising silicon and at least one second phase comprising carbon) or silicon-carbon-carbon (e.g., at least one first phase comprising silicon, at least one second phase comprising carbon, and at least one third phase comprising carbon) composite material.
• Silicon particles can increase the specific lithium insertion capacity of the composite material. When silicon absorbs lithium ions, it experiences a large volume increase on the order of 300+ volume percent which can cause electrode structural integrity issues. In addition to volumetric expansion related problems, silicon is not inherently electrically conductive, but becomes conductive when it is alloyed with lithium (e.g., lithiation). When silicon de-lithiates, the surface of the silicon loses electrical conductivity. Furthermore, when silicon de-lithiates, the volume decreases which results in the possibility of the silicon particle losing contact with the matrix. The dramatic change in volume also results in mechanical failure of the silicon particle structure, in turn, causing it to pulverize.
• lithium e.g., lithiation
• the composite material can include carbons such as graphite which contributes to the ability of the composite to absorb expansion and which is also capable of intercalating lithium ions adding to the storage capacity of the electrode (e.g., chemically active). Therefore, the composite material may include one or more types of carbon phases.
• the particle size (e.g., diameter or a largest dimension of the silicon particles) can be less than about 50 ⁇ m, less than about 40 ⁇ m, less than about 30 ⁇ m, less than about 20 ⁇ m, less than about 10 ⁇ m, less than about 1 ⁇ m, between about 10 nm and about 50 ⁇ m, between about 10 nm and about 40 ⁇ m, between about 10 nm and about 30 ⁇ m, between about 10 nm and about 20 ⁇ m, between about 0.1 ⁇ m and about 20 ⁇ m, between about 0.5 ⁇ m and about 20 ⁇ m, between about 1 ⁇ m and about 20 ⁇ m, between about 1 ⁇ m and about 15 ⁇ m, between about 1 ⁇ m and about 10 ⁇ m, between about 10 nm and about 10 ⁇ m, between about 10 nm and about 1 ⁇ m, less than about 500 nm, less than about 100 nm, about 100 nm, etc.
• an average particle size (or the average diameter or the average largest dimension) or a median particle size (or the median diameter or the median largest dimension) of the silicon particles can be less than about 50 ⁇ m, less than about 40 ⁇ m, less than about 30 ⁇ m, less than about 20 ⁇ m, less than about 10 ⁇ m, less than about 1 ⁇ m, between about 10 nm and about 50 ⁇ m, between about 10 nm and about 40 ⁇ m, between about 10 nm and about 30 ⁇ m, between about 10 nm and about 20 ⁇ m, between about 0.1 ⁇ m and about 20 ⁇ m, between about 0.5 ⁇ m and about 20 ⁇ m, between about 1 ⁇ m and about 20 ⁇ m, between about 1 ⁇ m and about 15 ⁇ m, between about 1 ⁇ m and about 10 ⁇ m, between about 10 nm and about 10 ⁇ m, between about
• the silicon particles may have a distribution of particle sizes. For example, at least about 95 %, at least about 90 %, at least about 85 %, at least about 80 %, at least about 70 %, or at least about 60 % of the particles may have the particle size described herein.
• the amount of silicon provided in the mixture or in the composite material can be greater than zero percent by weight of the mixture and/or composite material.
• the amount of silicon can be within a range of from about 0 % to about 99 % by weight of the composite material, including greater than about 0 % to about 99 % by weight, greater than about 0 % to about 95 % by weight, greater than about 0 % to about 90 %, greater than about 0 % to about 35 % by weight, greater than about 0 % to about 25 % by weight, from about 10 % to about 35 % by weight, at least about 30 % by weight, from about 30 % to about 99 % by weight, from about 30 % to about 95 % by weight, from about 30 % to about 90 % by weight, from about 30 % to about 80 % by weight, at least about 50 % by weight, from about 50 % to about 99 % by weight, from about 50 % to about 95 % by weight, from about 50 % to about 95 %
• the silicon particles may or may not be pure silicon.
• the silicon particles may be substantially silicon or may be a silicon alloy.
• the silicon alloy includes silicon as the primary constituent along with one or more other elements.
• micron-sized silicon particles can provide good volumetric and gravimetric energy density combined with good cycle life.
• silicon particles can have an average particle size or a median particle size in the micron range and a surface including nanometer-sized features.
• the silicon particles can have an average particle size (e.g., average diameter or average largest dimension) or a median particle size (e.g., median diameter or median largest diameter) between about 0.1 ⁇ m and about 30 ⁇ m or between about 0.1 ⁇ m and all values up to about 30 ⁇ m.
• the silicon particles can have an average particle size or a median particle size between about 0.1 ⁇ m and about 20 ⁇ m, between about 0.5 ⁇ m and about 25 ⁇ m, between about 0.5 ⁇ m and about 20 ⁇ m, between about 0.5 ⁇ m and about 15 ⁇ m, between about 0.5 ⁇ m and about 10 ⁇ m, between about 0.5 ⁇ m and about 5 ⁇ m, between about 0.5 ⁇ m and about 2 ⁇ m, between about 1 ⁇ m and about 20 ⁇ m, between about 1 ⁇ m and about 15 ⁇ m, between about 1 ⁇ m and about 10 ⁇ m, between about 5 ⁇ m and about 20 ⁇ m, etc.
• the average particle size or the median particle size can be any value between about 0.1 ⁇ m and about 30 ⁇ m, e.g., 0.1 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, and 30 ⁇ m.
• the nanometer-sized features can include an average feature size (e.g., an average diameter or an average largest dimension) between about 1 nm and about 1 mm, between about 1 nm and about 750 nm, between about 1 nm and about 500 nm, between about 1 nm and about 250 nm, between about 1 nm and about 100 nm, between about 10 nm and about 500 nm, between about 10 nm and about 250 nm, between about 10 nm and about 100 nm, between about 10 nm and about 75 nm, or between about 10 nm and about 50 nm.
• the features can include silicon.
• the amount of carbon obtained from the precursor can be about 50 weight percent from polyamic acid.
• the amount of carbon obtained from the precursor in the composite material can be greater than 0 % to about 95 % by weight such as about 1 % to about 95 % by weight, about 1 % to about 90 % by weight, 1 % to about 80% by weight, about 1 % to about 70 % by weight, about 1 % to about 60 % by weight, about 1 % to about 50 % by weight, about 1 % to about 40 % by weight, about 1 % to about 30 % by weight, about 5 % to about 95 % by weight, about 5 % to about 90 % by weight, about 5 % to about 80 % by weight, about 5 % to about 70 % by weight, about 5 % to about 60 % by weight, about 5 % to about 50 % by weight, about 5 % to about 40 % by weight, about 5 % to about 30 % by weight, about 10 % to about 95 % by weight such as
• the carbon from the precursor can be hard carbon.
• Hard carbon can be a carbon that does not convert into graphite even with heating in excess of 2800 degrees Celsius. Precursors that melt or flow during pyrolysis convert into soft carbons and/or graphite with sufficient temperature and/or pressure. Hard carbon may be selected since soft carbon precursors may flow and soft carbons and graphite are mechanically weaker than hard carbons.
• Other possible hard carbon precursors can include phenolic resins, epoxy resins, and other polymers that have a very high melting point or are crosslinked.
• the amount of hard carbon in the composite material can have a value within a range of greater than 0 % to about 95 % by weight such as about 1 % to about 95% by weight, about 1 % to about 90% by weight, about 1 % to about 80% by weight, about 1 % to about 70 % by weight, about 1 % to about 60 % by weight, about 1 % to about 50 % by weight, about 1 % to about 40 % by weight, about 1 % to about 30 % by weight, about 5 % to about 95% by weight, about 5 % to about 90 % by weight, about 5 % to about 80% by weight, about 5 % to about 70 % by weight, about 5 % to about 60 % by weight, about 5 % to about 50 % by weight, about 5 % to about 40 % by weight, about 5 % to about 30 % by weight, about 10 % to about 95% by weight, about 10 % to about 90 % by weight, about 10 % to about 10 % to about
• the amount of hard carbon in the composite material can be about 1 % by weight, about 5 % by weight, about 10 % by weight, about 20 % by weight, about 30 % by weight, about 40 % by weight, about 50 % by weight, or more than about 50 % by weight.
• the hard carbon phase is substantially amorphous.
• the hard carbon phase is substantially crystalline.
• the hard carbon phase includes amorphous and crystalline carbon.
• the hard carbon phase can be a matrix phase in the composite material.
• the hard carbon can also be embedded in the pores of the additives including silicon.
• the hard carbon may react with some of the additives to create some materials at interfaces. For example, there may be a silicon carbide layer between silicon particles and the hard carbon.
• heating the mixture to a desired pyrolysis temperature may further result in the surface modification of silicon particles present in the mixture.
• pyrolysis of the mixture may result in the formation of a surface coating on at least 50% of the silicon particles present in the mixture.
• pyrolysis of the mixture may result in the formation of a surface coating on at least 60%, 70%, 80%, 90% or 99% of the silicon particles present in the mixture.
• the surface coatings form a substantially continuous layer on the silicon particles.
• the carbonized precursor or resin may contact the surface of the silicon particles.
• the carbonized precursor in contact with the silicon particle surface may be one or more types of carbon phases resulting from pyrolysis of the precursor.
• the one or more types of carbon phases of the carbonized precursor in contact with the silicon particle surface may react with the silicon particles during pyrolysis to thereby form silicon carbide on the silicon particle surface. Therefore, in some embodiments, the surface coatings may comprise carbon, silicon carbide, and/or a mixture of carbon and silicon carbide.
• the silicon particles present in the mixture may comprise a native silicon oxide (SiO, SiO2, SiOx) surface layer.
• the carbonized precursor in contact with the silicon particle surface may react with the naturally occurring native silicon oxide surface layer to form silicon carbide.
• the carbonized precursor in contact with the silicon particle surface may react with substantially all of the native silicon oxide layer to form silicon carbide. Therefore, the surface coatings on the silicon particles may comprise, in some embodiments, carbon and silicon carbide, wherein the surface coating is substantially free of silicon oxide.
• a first portion of the surface coatings may comprise silicon carbide while a second portion may comprise a mixture of silicon carbide and carbon.
• the carbonized precursor in contact with the silicon particle surface may not fully convert the native silicon oxide layer to silicon carbide, and the resultant surface coating or coatings may comprise carbon, silicon carbide, and one or more silicon oxides, such as SiO, SiO2, and SiOx.
• the carbonized precursor in contact with the silicon particle surface may be completely reacted, resulting in surface coatings that comprise silicon carbide.
• substantially all of the surface coatings may comprise silicon carbide.
• such surface coatings may be substantially free of silicon oxide and/or carbon.
• the pyrolyzed mixture can include silicon particles having carbon and/or silicon carbide surface coatings creating a silicon-carbon- silicon carbide (e.g., at least one first phase comprising silicon, at least one second phase comprising carbon, and at least a third phase comprising silicon carbide) or silicon-carbon- carbon-silicon carbide (e.g., at least one first phase comprising silicon, at least one second phase comprising carbon, at least one third phase comprising carbon, and at least a fourth phase comprising silicon carbide) composite material.
• silicon-carbon- silicon carbide e.g., at least one first phase comprising silicon, at least one second phase comprising carbon, and at least a third phase comprising silicon carbide
• silicon-carbon- carbon-silicon carbide e.g., at least one first phase comprising silicon, at least one second phase comprising carbon, at least one third phase comprising carbon, and at least a fourth phase comprising silicon carbide
• surface coatings on the silicon particles described herein can help to constrain the outward expansion of the silicon particle during lithiation. By constraining outward particle expansion during lithiation, the surface coatings can help prevent mechanical failure of the silicon particles and ensure good electrical contact. The surface coatings can further enhance the electronic charge transfer within the electrode. Controlled and optimized surface modification of silicon particles in the anode may also significantly improve capacity retention during cycling of an associated battery cell.
• the surface coatings substantially affect the reactions that occur between the anode materials and the electrolyte within a battery.
• the surface coatings can help reduce unwanted reactions.
• the formed surface coatings and the removal of unwanted native oxide (SiO 2 ) via conversion into more stable and unreactive SiC can provide higher reversible capacity with minimized irreversible capacity loss.
• Irreversible capacity loss can be due to formation and build-up of a solid electrolyte interface (SEI) layer that consumes lithium. This becomes a more prominent issue for silicon particles because nano- and micro-scale silicon particles have large surface areas and larger silicon particles tend to pulverize during lithiation and delithiation which can introduce additional particle surface area.
• SEI solid electrolyte interface
• Figures 1B is a schematic illustration of the formation of silicon carbide on a silicon particle as described above.
• a silicon particle comprising a native silicon oxide surface layer is provided in a mixture comprising a precursor as described above.
• the mixture is pyrolyzed in a reducing atmosphere.
• a reducing atmosphere, a vacuum and/or flowing gas including H2, CO, or hydrocarbon gas can be used.
• the mixture is heated to about 500 °C to about 1350 °C.
• the mixture is heated to about 800 °C to about 1200 °C.
• the mixture is heated to about 1175 °C.
• the pyrolyzed precursor in contact with the surface of the silicon particle reacts with the native silicon oxide layer of the silicon particle to form silicon carbide.
• the carbonized precursor in contact with the silicon particle surface is depicted here as continuous and conformal, but may not be continuous or conformal in some other embodiments.
• the silicon carbide layer formed from the reaction between the native silicon oxide layer and the carbonized precursor in contact with the silicon particle surface may take the form of a coating or dispersion within the composite anode film. As shown in Figure 1B, in some embodiments the silicon carbide may not be continuous or conformal on the silicon particle, however in some other embodiments the silicon carbide may be a continuous and/or conformal coating.
• graphite particles are added to the mixture.
• graphite can be an electrochemically active material in the battery as well as an elastic deformable material that can respond to volume change of the silicon particles.
• Graphite is the preferred active anode material for certain classes of lithium-ion batteries currently on the market because it has a low irreversible capacity. Additionally, graphite is softer than hard carbon and can better absorb the volume expansion of silicon additives.
• the particle size (e.g., a diameter or a largest dimension) of the graphite particles can be between about 0.5 microns and about 20 microns.
• All, substantially all, or at least some of the graphite particles may comprise the particle size (e.g., diameter or largest dimension) described herein.
• an average or median particle size (e.g., diameter or largest dimension) of the graphite particles can be between about 0.5 microns and about 20 microns.
• the graphite particles may have a distribution of particle sizes. For example, at least about 95 %, at least about 90 %, at least about 85 %, at least about 80 %, at least about 70 %, or at least about 60 % of the particles may have the particle size described herein.
• the composite material can include graphite particles in an amount greater than 0 % and less than about 80 % by weight, including from about 40 % to about 75 % by weight, from about 5 % to about 30 % by weight, from about 5 % to about 25 % by weight, from about 5 % to about 20 % by weight, from about 5 % to about 15 % by weight, etc.
• conductive particles which may also be electrochemically active are added to the mixture. Such particles can enable both a more electronically conductive composite as well as a more mechanically deformable composite capable of absorbing the large volumetric change incurred during lithiation and de-lithiation.
• a particle size (e.g., diameter or a largest dimension) of the conductive particles can be between about 10 nanometers and about 7 micrometers. All, substantially all, or at least some of the conductive particles may comprise the particle size (e.g., diameter or largest dimension) described herein.
• an average or median particle size (e.g., diameter or largest dimension) of the conductive particles can be between about 10 nm and about 7 micrometers.
• the conductive particles may have a distribution of particle sizes. For example, at least about 95 %, at least about 90 %, at least about 85 %, at least about 80 %, at least about 70 %, or at least about 60 % of the particles may have the particle size described herein.
• the mixture can include conductive particles in an amount greater than zero and up to about 80 % by weight.
• the composite material can include about 45 % to about 80 % by weight.
• the conductive particles can be conductive carbon including carbon blacks, carbon fibers, carbon nanofibers, carbon nanotubes, etc. Many carbons that are considered as conductive additives that are not electrochemically active become active once pyrolyzed in a polymer matrix.
• the conductive particles can be metals or alloys including copper, nickel, or stainless steel.
• an electrode can include a composite material described herein. For example, a composite material can form a self-supported monolithic electrode.
• the pyrolysed carbon phase (e.g., hard carbon phase) of the composite material can hold together and structurally support the particles that were added to the mixture.
• the self-supported monolithic electrode does not include a separate collector layer and/or other supportive structures.
• the composite material and/or electrode does not include a polymer beyond trace amounts that remain after pyrolysis of the precursor.
• the composite material and/or electrode does not include a non-electrically conductive binder.
• the composite material may also include porosity, such as about 1 % to about 70 % or about 5 % to about 50 % by volume porosity. For example, the porosity can be about 5% to about 40% by volume porosity.
• the composite material can be attached to a current collector.
• the composite material may also be formed into a powder.
• the composite material can be ground into a powder.
• the composite material powder can be used as an active material for an electrode.
• the composite material powder can be deposited on a collector in a manner similar to making a conventional electrode structure, as known in the industry.
• an electrode in a battery or electrochemical cell can include a composite material, including composite material with the silicon particles described herein.
• the composite material can be used for the anode and/or cathode.
• the battery is a lithium ion battery.
• the battery is a secondary battery, or in other embodiments, the battery is a primary battery.
• the full capacity of the composite material may not be utilized during use of the battery to improve life of the battery (e.g., number charge and discharge cycles before the battery fails or the performance of the battery decreases below a usability level).
• a composite material with about 70 % by weight silicon particles, about 20 % by weight carbon from a precursor, and about 10 % by weight graphite may have a maximum gravimetric capacity of about 3000 mAh/g, while the composite material may only be used up to an gravimetric capacity of about 550 to about 1500 mAh/g.
• the maximum gravimetric capacity of the composite material may not be utilized, using the composite material at a lower capacity can still achieve a higher capacity than certain lithium ion batteries.
• the composite material is used or only used at a gravimetric capacity below about 70 % of the composite material’s maximum gravimetric capacity.
• the composite material is not used at a gravimetric capacity above about 70 % of the composite material’s maximum gravimetric capacity.
• the composite material is used or only used at a gravimetric capacity below about 50 % of the composite material’s maximum gravimetric capacity or below about 30 % of the composite material’s maximum gravimetric capacity.
• silicon particles for use in battery electrodes (e.g., anodes and cathodes).
• Anode electrodes currently used in the rechargeable lithium-ion cells typically have a specific capacity of approximately 200 milliampere hours per gram (including the metal foil current collector, conductive additives, and binder material).
• Graphite the active material used in most lithium ion battery anodes, has a theoretical energy density of 372 milliampere hours per gram (mAh/g).
• silicon has a high theoretical capacity of 4200 mAh/g.
• Silicon swells in excess of 300% upon lithium insertion. Because of this expansion, anodes including silicon should be able to expand while allowing for the silicon to maintain electrical contact with the silicon.
• Some embodiments provide silicon particles that can be used as an electro- chemically active material in an electrode.
• the electrode may include binders and/or other electro-chemically active materials in addition to the silicon particles.
• the silicon particles described herein can be used as the silicon particles in the composite materials described herein.
• an electrode can have an electro-chemically active material layer on a current collector, and the electro-chemically active material layer includes the silicon particles.
• the electro-chemically active material may also include one or more types of carbon.
• the silicon particles described herein can improve performance of electro-chemically active materials such as improving capacity and/or cycling performance. Furthermore, electro-chemically active materials having such silicon particles may not significantly degrade as a result of lithiation of the silicon particles.
• the silicon particles can have an average particle size, for example an average diameter or an average largest dimension, between about 10 nm and about 40 ⁇ m as described herein. Further embodiments can include average particle sizes of between about 1 ⁇ m and about 15 ⁇ m, between about 10 nm and about 1 ⁇ m, and between about 100 nm and about 10 ⁇ m. Silicon particles of various sizes can be separated by various methods such as by air classification, sieving or other screening methods. For example, a mesh size of 325 can be used separate particles that have a particle size less than about 44 ⁇ m from particles that have a particle size greater than about 44 ⁇ m.
• the silicon particles may have a distribution of particle sizes.
• at least about 90% of the particles may have particle size, for example a diameter or a largest dimension, between about 10 nm and about 40 ⁇ m, between about 1 ⁇ m and about 15 ⁇ m, between about 10 nm and about 1 ⁇ m, and/or larger than 200 nm.
• the silicon particles may have an average surface area per unit mass of between about 1 to about 100 m 2 /g, about 1 to about 80 m 2 /g, about 1 to about 60 m 2 /g, about 1 to about 50 m 2 /g, about 1 to about 30 m 2 /g, about 1 to about 10 m 2 /g, about 1 to about 5 m 2 /g, about 2 to about 4 m 2 /g, or less than about 5 m 2 /g.
• the silicon particles are at least partially crystalline, substantially crystalline, and/or fully crystalline. Furthermore, the silicon particles may be substantially pure silicon.
• the silicon particles described herein for some embodiments can generally have a larger average particle size.
• the average surface area of the silicon particles described herein can be generally smaller.
• the lower surface area of the silicon particles described herein may contribute to the enhanced performance of electrochemical cells.
• Typical lithium ion type rechargeable battery anodes would contain nano-sized silicon particles.
• smaller silicon particles such as those in nano-size ranges
• the silicon particles are milled to reduce the size of the particles. Sometimes the milling may result in roughened or scratched particle surface, which also increases the surface area.
• FIGS. 2A and 2B are SEM micrographs of an example embodiment of silicon particles milled-down from larger silicon particles. As shown in the figures, certain embodiments may have a roughened surface.
• certain embodiments include silicon particles with surface roughness in nanometer-sized ranges, e.g., micron-sized silicon particles with nanometer-sized features on the surface.
• Figures 2C and 2D are SEM micrographs of an example embodiment of such silicon particles.
• silicon particles can have an average particle size (e.g., an average diameter or an average largest dimension) in the micron range (e.g., as described herein, between about 0.1 ⁇ m and about 30 ⁇ m) and a surface including nanometer-sized features (e.g., as described herein, between about 1 nm and about 1 mm, between about 1 nm and about 750 nm, between about 1 nm and about 500 nm, between about 1 nm and about 250 nm, between about 1 nm and about 100 nm, between about 10 nm and about 500 nm, between about 10 nm and about 250 nm, between about 10 nm and about 100 nm, between about 10 nm and about 75 nm, or between about 10 nm and about 50 nm).
• the features can include silicon.
• silicon particles with a combined micron/nanometer-sized geometry can have a higher surface area than milled-down particles.
• the silicon particles to be used can be determined by the desired application and specifications.
• the total surface area of the particles can be more similar to micron-sized particles than to nanometer-sized particles.
• micron-sized silicon particles e.g., silicon milled-down from large particles
• nanometer-sized silicon particles typically have an average surface area per unit mass of over about 0.5 m 2 /g and less than about 2 m 2 /g (for example, using Brunauer Emmet Teller (BET) particle surface area measurements)
• BET Brunauer Emmet Teller
• Certain embodiments described herein can have an average surface area per unit mass between about 1 m 2 /g and about 30 m 2 /g, between about 1 m 2 /g and about 25 m 2 /g, between about 1 m 2 /g and about 20 m 2 /g, between about 1 m 2 /g and about 10 m 2 /g, between about 2 m 2 /g and about 30 m 2 /g, between about 2 m 2 /g and about 25 m 2 /g, between about 2 m 2 /g and about 20 m 2 /g, between about 2 m 2 /g and about 10 m 2 /g, between about 3 m 2 /g and about 30 m 2 /g, between about 3 m 2 /g and about 25 m 2 /g, between about 3 m 2 /g and about 20 m 2 /g, between about 3 m 2 /g and about 10 m 2 /g (e.g., between about 3 m 2
• FIG. 2E illustrates an example method 200 of forming certain embodiments of the composite material.
• the method 200 includes providing a plurality of silicon particles (for example, silicon particles having an average particle size between about 0.1 ⁇ m and about 30 ⁇ m and a surface including nanometer-sized features), block 210.
• the method 200 further includes forming a mixture that includes a precursor and the plurality of silicon particles, block 220.
• the method 200 further includes pyrolysing the precursor, block 230, to convert the precursor into one or more types of carbon phases to form the composite material.
• silicon with the characteristics described herein can be synthesized as a product or byproduct of a Fluidized Bed Reactor (FBR) process.
• FBR Fluidized Bed Reactor
• useful material can be grown on seed silicon material.
• particles can be removed by gravity from the reactor.
• Some fine particulate silicon material can exit the reactor from the top of the reactor or can be deposited on the walls of the reactor.
• the material that exits the top of the reactor or is deposited on the walls of the reactor can have nanoscale features on a microscale particle.
• a gas e.g., a nitrogen carrier gas
• a gas e.g., a nitrogen carrier gas
• the silicon material can be a plurality of granular silicon.
• the gas can be passed through the silicon material at high enough velocities to suspend the solid silicon material and make it behave as a fluid.
• the process can be performed under an inert atmosphere, e.g., under nitrogen or argon.
• silane gas can also be used, for example, to allow for metal silicon growth on the surface of the silicon particles.
• the growth process from a gas phase can give the silicon particles the unique surface characteristics, e.g., nanometer-sized features.
• silicon particles formed using the FBR process can advantageously acquire small features, e.g., in nanometer-sized ranges, that may not be as easily achievable in some embodiments of silicon particles formed by milling from larger silicon particles.
• the FBR process can be under an inert atmosphere, very high purity particles (for example, higher than 99.9999% purity) can be achieved. In some embodiments, purity of between about 99.9999% and about 99.999999% can be achieved.
• the FBR process can be similar to that used in the production of solar- grade polysilicon while using 85% less energy than the traditional Siemens method, where polysilicon can be formed as trichlorosilane decomposes and deposits additional silicon material on high-purity silicon rods at 1150oC. Because nanometer-sized silicon particles have been shown to increase cycle life performance in electrochemical cells, micron-sized silicon particles have not been contemplated for use as electrochemical active materials in electrochemical cells.
• forming a mixture that includes a precursor and the plurality of silicon particles, block 220, and pyrolysing the precursor, block 230, to convert the precursor into one or more types of carbon phases to form the composite material can be similar to blocks 101 and 105 respectively, of method 100 described herein.
• pyrolysing e.g., at about 900 oC to about 1350 o C
• temperatures below the melting point of silicon e.g., at about 1414 oC
• certain micron- sized silicon particles with nanometer surface feature can achieve high energy density, and can be used in composite materials and/or electrodes for use in electro-chemical cells to improve performance during cell cycling.
• silicon particles may be used as electrochemically active material in an electrode.
• the silicon particles may be used in silicon-carbon composite electrodes.
• the electrodes can be formed by pyrolyzing a mixture comprising carbon precursor and silicon particles to convert the carbon precursor into one or more carbon phases to form a composite material film with the silicon particles distributed throughout the composite material film.
• the surfaces of the silicon particles can be modified to improve wetting by the carbon precursor, thereby improving the adhesion with the carbon precursor and decreasing the amount of porosity in the silicon-carbon interface.
• the silicon-carbon composite electrode can have greater physical strength, greater conductivity, and better cycling performance in batteries.
• FIG. 3A schematically illustrates an example surface modified silicon particle 300 that can be used as active material in silicon-composite electrodes, e.g., in lithium-ion batteries.
• the example silicon particle 300 comprises bulk material 301 and a surface 302.
• the surface 302 can be modified by silane treatment as will be described further and indicated by Si-O-Si bonds on the surface 302.
• bonds are illustrated as Si-O-Si-R, but may include other bonds, elements, and/or functional groups.
• the silicon particle 300 in Figure 3A is illustrated as having a circular cross-sectional shape such as for a spherical or cylindrical particle.
• “silicon particle” 300 described herein can have any regular or irregular cross-sectional shape and is not limited to a spherical or cylindrical particle.
• the silicon particle 300 can be any size as described herein, e.g., having a largest diameter or dimension from about 10 nm to about 50 ⁇ m, having a largest diameter or dimension from about 1 ⁇ m to about 50 ⁇ m, etc.
• the bulk material 301 can have any characteristic of any of the silicon particles described herein.
• the bulk material 301 may or may not be pure silicon.
• the bulk material 301 can be substantially silicon or can be a silicon alloy (e.g., silicon as the primary constituent along with one or more other elements).
• the bulk material 301 can be from about 90% pure silicon to about 99.9999% pure silicon.
• the bulk material 301 can be substantially pure silicon.
• the bulk material 301 can be at least partially crystalline, substantially crystalline, and/or fully crystalline.
• the surface 302 can include a native and/or artificially created oxide layer (e.g., SiO, SiO2, SiOx, SiOH). Surface oxidation may be done in the presence or absence of water, e.g., between about 100°C and about 1200°C.
• a native and/or artificially created oxide layer e.g., SiO, SiO2, SiOx, SiOH.
• Surface oxidation may be done in the presence or absence of water, e.g., between about 100°C and about 1200°C.
• the surface 302 can be modified using one or more silicon-containing organic compounds, e.g., organosilanes.
• organosilanes can react with the silicon’s native and/or artificially created oxide.
• one or more organosilanes can react with silanol groups on the silicon surface 302 to form bonds (e.g., Si-O-Si) between the silanol groups and organosilane.
• the organosilane may contain a range of functional groups, including but not limited to: silanols (R-Si-OH), silyl ethers (R-Si-OR’), silyl chlorides (R-Si-Cl), dialkylaminosilanes (R-Si-NR 2 ), silyl hydrides (R-SiH3), and/or cyclic azasilanes.
• The“R” region of the organosilane may have one or more functional groups tailored to the specific components used in the preparation of the silicon composite electrodes.
• an aminoalkyl functional group can be used, such as those present in 3- aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), or 2,2-dimethoxy-1,6-diaza-2-silacyclooctane. Shown below is the molecular structure of 3-aminopropyltriethoxysilane, a silyl ether with an amine function group.
• an epoxide linker may be used. Shown below is the molecular structure of an example epoxide linker, 5,6- epoxyhexyltriethoxysilane, a silyl ether with an epoxide functional group.
• an organosilane with an aromatic functional group may be used.
• An example of such an organosilane is benzyltriethoxysilane, a silyl ether with an aromatic function group. The molecular structure is shown below.
• the organosilane can include a silyl hydride (R- SiH 3 ).
• R- SiH 3 silyl hydride
• the molecular structure of dodecylsilane is shown below.
• the organosilane can include a dialkylaminosilane (R-Si-NR2).
• R-Si-NR2 dialkylaminosilane
• the silane-treated silicon particle 300 can include a silicon oxide surface reacted with one or more organosilanes.
• the surface 302 of the silicon particle 300 can include bonds between the surface silanol groups and organosilane.
• the general principle is that the silanol groups on the silicon particle surface 302 participate in nucleophilic substitution reactions with the organosilane.
• reaction mechanisms can involve a similar direct substitution reaction, producing an alcohol.
• reaction mechanisms can involve a two-step mechanism involving 1) hydrolysis of the silyl ether to produce an alcohol and a silanol and 2) a condensation reaction between the organosilanol and the particle surface silanol to form a new Si-O-Si bond and water as a byproduct.
• Similar nucleophilic substitution reaction mechanisms can apply to the dialkylaminosilanes (e.g., producing Si-O-Si and a secondary amine), silyl hydrides (e.g., forming hydrogen), or cyclic azasilanes (e.g., re-arranging to form linear organosilanes).
• Multifunctional silyl ethers for example, AEAPTMS
• silanols can participate in a certain amount of polymerization at the silicon surface, as each silanol (or hydrolyzed silyl ether) can condense to form Si-O-Si with another silanol.
• the surface modification can be carried out using several different approaches.
• the silicon may be suspended in a heated liquid containing a certain concentration of an organosilane.
• the liquid can be heated to a temperature in the range of about 50 o C to about 200 o C or any range within this range (e.g., about 50 o C to about 100 o C, about 50 o C to about 150 o C, about 50 o C to about 175 o C, about 75 o C to about 200 o C, about 100 o C to about 200 o C, about 150 o C to about 200 o C, etc.).
• This method can be used for silyl ethers and silyl chlorides.
• the liquid may be water, an organic solvent, or a mixture of water and organic solvents. In some instances, some water can be used for silyl ethers. In some instances, little or substantially no water can be used for silyl chlorides.
• the silicon may be modified by exposure to organosilane vapors, e.g., either while spread into thin layers in trays or while agitated in a reactor vessel. Other examples are possible.
• the amount of organosilane can be tied to the specific surface area of the silicon and/or the specific wetting surface of the organosilane.
• a silicon material with a specific surface area of 0.6m 2 /g and an organosilane with a specific wetting surface of 358m 2 /g can use a ratio of about 1.68g organosilane per kilogram of silicon in some instances.
• silane-treated silicon particles can be used to form certain embodiments of composite materials as described herein.
• the composite material can be used in an electrode for use in an electrochemical cell.
• Certain embodiments can include a composite material film.
• the composite material film can include any of the examples of composite material films described herein.
• the composite material film can have greater than 0% to about 99% by weight of silicon particles (e.g., about 50% to about 99% by weight, about 60% to about 99% by weight, about 70% to about 99% by weight, about 75% to about 99% by weight, about 80% to about 99% by weight, etc.), or greater than 0% and to about 95% by weight of silicon particles (e.g., about 50% to about 95% by weight, about 60% to about 95% by weight, about 70% to about 95% by weight, about 75% to about 95% by weight, about 80% to about 95% by weight, etc.).
• the silicon particles can include surface treated silicon particles and/or a combination of surface treated and untreated silicon particles.
• the treated or untreated silicon particles can include any of the silicon particles described herein (e.g., silicon particles with an average particle size from about 0.1 ⁇ m to about 40 ⁇ m, silicon particles with an average particle size from about 1 ⁇ m to about 20 ⁇ m, micron-sized silicon particles with nanometer-sized features, etc.).
• the organic portion of the organosilane can interact with carbon precursors via various mechanisms, e.g., depending on which organosilane and which precursor is used.
• an organosilane with a primary amine group such as AEAPTMS
• AEAPTMS a primary amine group
• a precursor containing a carboxylic acid group such as polyamic acid
• Other interactions are possible as well.
• the primary amine group in the organosilane may participate in hydrogen bonding with the carbonyl groups in the polyamic acid (or polyimide).
• the Si-O-Si bonds can be relatively thermally stable such that at least a Si-O-Si monolayer can remain on the silicon particle surface after pyrolysis, e.g., at about 900°C to about 1350°C.
• the Si-O-Si domain may be a few layers thick depending on the reaction conditions.
• the organic portion of the organosilane may pyrolyze following similar mechanisms to the carbon precursor, forming hydrogen gas, water, carbon monoxide, carbon dioxide, cyanide, and/or carbon, depending on the composition and the conditions.
• the composite material film can also have greater than 0% and to about 90% by weight of one or more types of carbon phases.
• the one or more types of carbon phases can be a substantially continuous phase. In some instances, the continuous phase can hold the composite material film together.
• the one or more types of carbon phases can be electrochemically active and/or electrically conductive. In some embodiments, the silicon particles can be distributed throughout the composite material film.
• the silicon particles can have surface coatings.
• the surface coatings can cover at least about 50%, 60%, 70%, 80%, 90%, or 99% of the silicon particles.
• the surface coatings can be a substantially continuous layer.
• the surface coatings can include silicon monoxide (SiO), silicon dioxide (SiO 2 ), and/or silicon oxide (SiO x ). During pyrolysis, some, substantially all, or all of the silicon oxide on the surface of the silicon particle may be converted into silicon carbide.
• the composite material film can include an interfacial region between the silicon particles and the one or more types of carbon phases.
• the interfacial region can include silicon, carbon, silicon oxide, silicon carbide, silicon oxycarbide, or a mixture of these materials, with or without dopants.
• the modified surfaces of the silicon particles can improve wetting by the carbon precursor, thereby improving the adhesion with the carbon precursor and decreasing porosity in the silicon-carbon interface.
• the interfacial region can include less than or equal to about 30%, 25%, 20%, 15%, 10%, or 5% porosity.
• the strength and conductivity of the composite material can increase.
• the composite material film can be self-supported.
• the composite material film can be attached to a current collector.
• the composite material film can be used as an electrode (e.g., anode or cathode).
• Figure 3B illustrates an example method 400 of forming certain embodiments of a composite material.
• the method 400 can include providing a mixture comprising a carbon precursor and silane-treated silicon particles, block 410.
• the method 400 can also include pyrolysing the precursor, e.g., to convert the precursor into one or more types of carbon phases, block 420.
• the silane-treated silicon particles can be added to a mixture comprising a carbon precursor.
• the silicon particles can be silane-treated using any embodiment described herein.
• the carbon precursor can include a polymer and a solvent.
• the polymer and solvent can include any of the polymers and solvents described herein.
• the method 400 can also include various steps such as casting the mixture on a substrate, drying the mixture to form a film, removing the film from the substrate, and placing the film in a hot press.
• the carbon precursor can be pyrolyzed as described herein to convert the precursor into one or more types of carbon phases.
• the silicon particles can be distributed throughout the composite material film.
• silane surface-treated silicon particles can have better wetting with polymeric binder solutions and a greater ability to adhere to polymeric materials.
• the adhesion is able to survive pyrolysis. In a silicon-carbon composite material, this can translate to less porosity, greater physical strength, and/or better cycling performance, e.g., in lithium-ion batteries.
• the increased SiO2 domain from multi-functional silyl ethers can produce an increased SiC domain which can provide additional structural integrity to various embodiments of silicon composites.
• the addition of an interfacial layer between the silicon and carbon does not increase the electrical resistance and/or harm electrochemical performance.
• the Si-O in silane can be reduced to form SiC which, per equation 1, can help in reducing Li loss to the SEI layer.
• NMP N-Methyl-2- pyrrolidone
• Example 1 a polyimide liquid precursor (PI 2611 from HD Microsystems corp.), graphite particles (SLP30 from Timcal corp.), conductive carbon particles (Super P from Timcal corp.), and silicon particles (from Alfa Aesar corp.) were mixed together for 5 minutes using a Spex 8000D machine in the weight ratio of 200:55:5:20. The mixture was then cast onto aluminum foil and allowed to dry in a 90 °C oven, to drive away solvents, e.g., NMP. This is followed by a curing step at 200 °C in a hot press, under negligible pressure, for at least 12 hours. The aluminum foil backing was then removed by etching in a 12.5% HCl solution.
• solvents e.g., NMP
• Example 2 silicon particles (from EVNANO Advanced Chemical Materials Co. Ltd.) were initially mixed with NMP using a Turbula mixer for a duration of one hour at a 1:9 weight ratio.
• Polyimide liquid precursor PI 2611 from HD Microsystems corp.
• graphite particles SLP30 from Timcal corp.
• carbon nanofibers CNF from Pyrograf corp.
• the mixture was then cast onto aluminum foil that was covered by a 21 ⁇ m thick copper mesh.
• the samples were then allowed to dry in a 90 °C oven to drive away solvents, e.g., NMP.
• Example 3 polyimide liquid precursor (PI 2611 from HD Microsystems corp.), and 325 mesh silicon particles (from Alfa Aesar corp.) were mixed together using a Turbula mixer for a duration of 1 hour in the weight ratios of 40:1. The mixture was then cast onto aluminum foil and allowed to dry in a 90 °C oven to drive away solvents, e.g., NMP. This was followed by a curing step at 200 °C in a hot press, under negligible pressure, for at least 12 hours. The aluminum foil backing was then removed by etching in a 12.5% HCl solution. The remaining film was then rinsed in DI water, dried and then pyrolyzed around an hour at 1175 °C under argon flow. The process resulted in a composition of 75% of PI 2611 derived carbon and 25% of silicon by weight.
• solvents e.g., NMP.
• Example 4 silicon microparticles (from Alfa Aesar corp.), polyimide liquid precursor (PI 2611 from HD Microsystems corp.), graphite particles (SLP30 from Timcal corp.), milled carbon fibers (from Fibre Glast Developments corp.), carbon nanofibers (CNF from Pyrograf corp.), carbon nanotubes (from CNANO Technology Limited), conductive carbon particles (Super P from Timcal corp.), conductive graphite particles (KS6 from Timca corp.) were mixed in the weight ratio of 20:200:30:8:4:2:1:15 using a vortexer for 5 minutes. The mixture was then cast onto aluminum foil.
• the samples were then allowed to dry in a 90 °C oven to drive away solvents, e.g., NMP. This was followed by a curing step at 200 °C in a hot press, under negligible pressure, for at least 12 hours.
• solvents e.g., NMP.
• the aluminum foil backing was then removed by etching in a 12.5% HCl solution.
• the remaining film was then rinsed in DI water, dried and then pyrolyzed for around an hour at 1175 °C under argon.
• the process resulted in a composition similar to the original mixture but with a PI 2611 derived carbon portion that was 7.5% the original weight of the polyimide precursor.
• Example 5 polyimide liquid precursor (PI 2611 from HD Microsystems corp.), and silicon microparticles (from Alfa Aesar corp.) were mixed together using a Turbula mixer for a duration of 1 hours in the weight ratio of 4:1. The mixture was then cast onto aluminum foil covered with a carbon veil (from Fibre Glast Developments Corporation) and allowed to dry in a 90 °C oven to drive away solvents, e.g., NMP. This was followed by a curing step at 200 °C in a hot press, under negligible pressure, for at least 12 hours. The aluminum foil backing was then removed by etching in a 12.5% HCl solution.
• solvents e.g., NMP
• the remaining film was then rinsed in DI water, dried and then pyrolyzed around an hour at 1175 °C under argon flow.
• the process resulted in a composition of approximately 23% of PI 2611 derived carbon, 76% of silicon by weight, and the weight of the veil being negligible.
• Example 6 polyimide liquid precursor (PI 2611 from HD Microsystems corp.), graphite particles (SLP30 from Timcal corp.), and silicon microparticles (from Alfa Aesar corp.) were mixed together for 5 minutes using a Spex 8000D machine in the weight ratio of 200:10:70. The mixture was then cast onto aluminum foil and allowed to dry in a 90 °C oven, to drive away solvents (e.g., NMP). The dried mixture was cured at 200 °C in a hot press, under negligible pressure, for at least 12 hours. The aluminum foil backing was then removed by etching in a 12.5% HCl solution.
• solvents e.g., NMP
• the remaining film was then rinsed in DI water, dried and then pyrolyzed at 1175 °C for about one hour under argon flow.
• the process resulted in a composition of 15.8% of PI 2611 derived carbon, 10.5% of graphite particles, 73.7% of silicon by weight.
• Example 7 PVDF and silicon particles (from EVNANO Advanced Chemical Materials Co), conductive carbon particles (Super P from Timcal corp.), conductive graphite particles (KS6 from Timcal corp.), graphite particles (SLP30 from Timcal corp.) and NMP were mixed in the weight ratio of 5:20:1:4:70:95. The mixture was then cast on a copper substrate and then placed in a 90 °C oven to drive away solvents, e.g., NMP. The resulting electrodes were then tested in a pouch cell configuration against a lithium NMC Oxide cathode. A typical cycling graph is shown in Figure 10.
• Figure 14 is a photograph of a 4.3 cm x 4.3 cm composite anode film without a metal foil support layer.
• the composite anode film has a thickness of about 30 microns and has a composition of about 15.8% of PI 2611 derived carbon, about 10.5% of graphite particles, and about 73.7% of silicon by weight.
• Figures 15-20 are scanning electron microscope (SEM) micrographs of a composite anode film.
• the compositions of the composite anode film were about 15.8% of PI 2611 derived carbon, about 10.5% of graphite particles, and about 73.7% of silicon by weight.
• Figures 15 and 16 show before being cycled (the out-of-focus portion is a bottom portion of the anode and the portion that is in focus is a cleaved edge of the composite film).
• Figures 17, 18, and 19 are SEM micrographs of a composite anode film after being cycled 10 cycles, 10 cycles, and 300 cycles, respectively.
• Figure 21 is an x-ray powder diffraction (XRD) graph of the sample silicon particles.
• the XRD graph suggests that the sample silicon particles were substantially crystalline or polycrystalline in nature.
• Figures 22-25 are scanning electron microscope (SEM) micrographs of the sample silicon particles. Although the SEM micrographs appear to show that the silicon particles may have an average particle size greater than the measured average particle size of about 300 nm, without being bound by theory, the particles are believed to have conglomerated together to appear to be larger particles.
• SEM scanning electron microscope
• Figure 26 is a chemical analysis of the sample silicon particles. The chemical analysis suggests that the silicon particles were substantially pure silicon.
• Figures 27A and 27B are example particle size histograms of two micron- sized silicon particles with nanometer-sized features.
• the particles were prepared from a FBR process.
• Example silicon particles can have a particle size distribution.
• at least 90% of the particles may have a particle size, for example, a diameter or a largest dimension, between about 5 ⁇ m and about 20 ⁇ m (e.g., between about 6 ⁇ m and about 19 ⁇ m).
• At least about 50% of the particles may have a particle size between about 1 ⁇ m and about 10 ⁇ m (e.g., about 2 ⁇ m and about 9 ⁇ m).
• Figure 28 is a plot of discharge capacity during cell cycling comparing two types of example silicon particles.
• the performance of four samples of silicon particles (micron-sized particles with nanometer-sized features) prepared by the FBR process are compared with five samples of silicon particles prepared by milling-down larger silicon particles.
• certain embodiments of silicon particles with the combined micron/nanometer geometry e.g., prepared by the FBR process
• can have enhanced performance over various other embodiments of silicon particles e.g., micron-sized silicon particles prepared by milling down from larger particles.
• the type of silicon particles to use can be tailored for the intended or desired application and specifications. Examples of Silane-Treated Silicon Particles
• silicon was added to a 2% solution of N-(2- aminoethyl)-3-aminopropyltrimethoxysilane in water, refluxed at 100°C for 2 hours, and dried at 200°C for 16h. The resulting cake was pulverized and analyzed with X-ray Photoelectron Spectroscopy (XPS) to confirm the surface had been modified with the organosilane.
• XPS X-ray Photoelectron Spectroscopy
• silicon was placed in a glass vessel and combined with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, with a component ratio of 0.4% organosilane to silicon by weight.
• the materials were agitated at 90°C for 4 hours under atmospheric pressure. This produced a loosely agglomerated powder.
• Figure 29 shows a region of the X-ray Photoelectron Spectroscopy (XPS) spectra of the silane-treated and untreated silicon samples.
• the spectra for the examples treated in water (with and without silane) are shown as“Moisture-processed,” and the spectra for the examples placed in a glass vessel under atmospheric pressure (with and without silane) are shown as“Rotovap-processed.”
• the spectra show increased carbon content for the silane-treated silicon.
• the rotovap-processed silane-treated silicon has a higher peak than the moisture-processed silane-treated silicon.
• the rotovap-process was done in a closed vessel at 90°C where the silane vapors do not escape, thereby increasing the probability of reaction with the silicon.
• silane-treated silicon moisture-processed and rotovap-processed
• NMP nitrogen-containing polyphenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-N-phenyl-
• a 15 ⁇ m thick copper foil was coated with polyamide-imide (applied as a 6wt% varnish in NMP, dried 16h at 110°C under vacuum).
• the silicon-carbon composite film was laminated to the coated copper using a heated hydraulic press (50 seconds, 300°C, 4000 psi), forming the finished silicon-composite electrode.
• the silicon- carbon composite electrodes were inspected and analyzed.
• Figure 30A is a scanning electron microscope with focused ion beam (SEM-FIB) micrograph of a cross-section of an example silicon-carbon composite material made with untreated silicon particles.
• Figure 30B is a SEM-FIB micrograph of a cross- section of the example silicon-carbon composite material made with the silane-treated silicon particles.
• the composite material made with silane-treated silicon had fewer porosity in the silicon-carbon interfacial region compared with the composite material made with untreated silicon.
• silicon was added to a 2.5% solution of N-(2- aminoethyl)-3-aminopropyltrimethoxysilane in N-methyl-2-pyrollidone and milled with zirconia media for 6 hours.
• the resulting slurry was combined with graphite and polyamic acid resin, and coated onto a PET substrate.
• the film was converted into a silicon-carbon composite electrode.
• the silicon-carbon composite electrodes were assembled into lithium-ion cells, containing cathodes, separator, and electrolyte solution.
• the cathodes were comprised of 15 ⁇ m aluminum foil coated with a 23mg/cm 2 , 3.02g/cc film containing 95% NCM622, 2.5% conductive carbon additive, and 2.5% PVdF.
• the separator was a 16 ⁇ m porous polypropylene membrane, coated with 3.5 ⁇ m thick films consisting of a mixture of PVdF and PMMA.
• the electrolyte solution included 1.2M LiPF6 in organic carbonates.
• the cell design had a nominal capacity of 710mAh.
• the cells were tested using constant current/constant voltage charge profiles and constant current discharge profiles. The upper voltage limit was 4.1V, and the lower voltage limit was 2.75V.
• the current was 1.42A for the charge step, with a current limit of 0.035A for the constant voltage portion, and a current of 0.35A for the discharge step. Every 50 cycles, a characterization cycle was performed, with a charge current of 0.35A and a discharge current of 0.14A.
• Figure 31 shows a graph of capacity retention versus cycle number for full-cells comprising silane-treated silicon particles compared with full-cells comprising untreated silicon particles.
• the results for the full-cells fabricated with moisture-processed and rotovap-processed silane-treated silicon are shown as“Silane Treated Si.”
• the results for the full-cells fabricated with the other silane treatment e.g., adding organosilane into the slurry
• the two different organosilane (N-(2- aminoethyl)-3-aminopropyltrimethoxysilane) treatment conditions provided improved capacity retention over untreated silicon, tested in full-cells vs NCM622, 4.1V to 2.75V.
• Figure 32 shows a graph of capacity retention versus cycle number for full-cells comprising silane-treated silicon particles (using the method of adding organosilane into the slurry) compared with full-cells comprising untreated silicon particles in a follow-up trial.
• the results confirmed the performance improvement for organosilane-treated silicon under slightly modified test conditions (4.2V upper voltage cut-off instead of 4.1V, and with characterization cycles every 100 cycles).

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